This application claims priority of European application EP99810966.4, filed on Oct. 22, 1999, and whose contents are hereby incorporated by way of reference.
The present invention concerns a measuring device, notably a comparator for measuring and comparing lengths or angles.
An example of comparator is represented in the FIGS. 1 and 2. This comparator 1 comprises a casing 2, here of cylindrical shape, and a sensing probe 3 whose tip 30 is intended to come into contact with the object to be measured or checked. A mechanical, optoelectronic and/or electronic measuring system makes it possible to determine the longitudinal position of the measuring probe and to display it, for example on a hand dial or on a LCD 4. The comparator is generally provided with one or several sockets 8, 9 of normed dimensions enabling it to be attached to a machine or an external device. Comparators with electronic displays such as that represented are furthermore provided with a battery compartment 6, operating keys 5 as well as possibly a serial interface 7, for example an optoelectronic interface.
In the comparator represented in FIGS. 1 and 2, bearings 80, 90 are provided to allow an accurate sliding and guiding of the probe 3. In this example, the bearing 90 is worked directly in the upper socket 9 whereas the lower bearing 80 is mounted in the lower socket 8.
The comparator represented is fitted with a metallic housing whose outer sides have been surface-treated, notably for aesthetic reasons. Tightness is only partially ensured thanks to a solid casing 2 and a bottom 26 screwed or notched onto that casing and protecting the comparator""s inner mechanism from sprayings of liquid. The device illustrated in FIG. 1 and 2 must therefore be kept clean to function properly and is thus poorly adapted to operating in an environment that is humid or subject to the spraying of dust, lubricant or cutting oil for example. In particular, it is important to ensure that the measuring system inside the comparator is free from all humidity.
Patent application DE3211118 describes another comparator similar to that represented in FIGS. 1 and 2. DE19738316 shows a comparator in which the sensing probe is guided by grooves worked inside the casing.
It is an aim of the present invention to propose a comparator that is improved over the comparators of the prior art. A purpose of the present invention is also to propose a comparator that is more economical, more accurate, more airtight and watertight, more resistant and/or comprising fewer components than the comparator illustrated in FIGS. 1 and 2.
According to the invention, these aims are achieved by means of a comparator with the characteristics of the independent claims, variants of preferred embodiments being moreover described in the dependent claims.
According to the invention, these aims are achieved notably by moving the probe""s travel bearings closer to one another. The invention thus proposes to use a distance I between the bearings that is less than the housing""s diameter. This characteristic makes it possible to reduce the bending of the probe""s rod and thus to increase accuracy.
According to another characteristic of the invention, these aims are also achieved by using bearings worked directly into the comparator""s casing. This characteristic allows to reduce the number of components, and therefore the cost, and to diminish the sum of manufacture and assembly tolerances of the different components, which also makes it possible to improve accuracy. This characteristic also allows the distance I between the bearings to be reduced.
According to another characteristic of the invention, these aims are also achieved by using a housing covering the outer sides of the comparator""s metallic casing. The housing makes it possible to solve the tightness problems. Furthermore, the housing makes it possible to increase the external diameter of the comparator and thus to use a display 4 that is larger and more legible, without having to increase the distance I between the bearings which is determined by the diameter of the metallic casing. The housing is preferably of synthetic material and can be held by the comparator""s sockets, allowing for a simple construction. By disposing it so as to cover completely the metallic casing, it is furthermore possible to dispense with the expensive surface treatment of the casing, which allows the costs to be reduced without having to give up an attractive design.